1. Field of the Invention
This invention relates to the field of data communications. More specifically, it relates to the field of serial port access to registers and to the field of serial port access to multiple registers.
2. The Prior Art
Numerous applications take advantage of register-based serial ports. A device may contain a plurality of registers which communicate with a serial port from which data is written into the registers and to which data is read from the registers. A system may include a plurality of such devices each having its own plurality of registers.
An example of a system in the prior art to which the present invention is relevant is the IEEE Standard 802.3u, clause 22. IEEE standard 802.3u defines the logical, electrical, and mechanical characteristics for the Reconciliation sublayer and Media Independent Interface (MII) between CSMA/CD media access controllers and various physical layer devices.
The physical layer devices in this system may have a management port which is a register-based serial port. During system operation, data may be written to and read from individual ones of the registers in the physical devices.
Communication in such a system is packet based. A packet of information asserted on the serial port contains a read/write operation identifier, an address of the physical device containing the register of interest, an address of the register of interest within that device, and, if the operation is a write operation, the data to be written into the register. As will be appreciated by those of ordinary skill in the art, the packet also contains bits used to synchronize the receipt of the information contained therein.
While these systems have performed satisfactorily in the prior art, they are inefficient when read or write operations to multiple registers are to be performed. In order to read or write from or to multiple registers in the same physical device, individual packets must be asserted on the bus to which the serial port is connected. This necessarily consumes valuable bandwidth.